#include<iostream>
using namespace std;
int f[30010];
int v[30], w[30];
int n, m;
int main()
{
	cin >> m >> n;
	for (int i = 1; i <= n; i++) {
		cin >> v[i] >> w[i];
		w[i] *= v[i];
	}
	for (int i = 1; i <= n; i++) {
		for (int j = m; j >= v[i]; j--) {
			f[j] = max(f[j], f[j - v[i]] + w[i]);
		}
	}
	cout << f[m] << endl;
	return 0;
}